A loose exhaust valve is a happy exhaust valve.

[burning1]

Quick update on this thread... I opened my valves up to the spec that gsJack posted at the beginning of my last race season. I haven't been in there since, but I can confirm that running the clearance he recommended didn't seem to cause me any obvious problems under the abuse of racing and track riding. And that's with some pretty extended runs at 10K RPM. I'll update again when I inspect the clearance.

Only potential issue is the loss of .001 inch of lift, but to be honest, keeping the engine alive and avoiding spending a lot of time wrenching on it is worth it to me. In my experience, every time you open a bike up, you have a chance of creating an oil leak, or other problem.

FWIW, Megacycles recommends .004 inches of clearance for all of their higher lift cams.

[gsJack]

Timely thread update burning1, I just did my annual valve check and changed one shim on an exhaust valve from 250-245 so the minimum shim in this 02 GS with 86k miles on it is a 245 now.  It's been set to my greater exhaust valve tolerances since my 40k mile check they have held up well.  I put a minimum 215 thick shim in my 97 GS at 76.8k miles and parked it at 80k miles.  I expect to run this bike to 100k miles without further valve checks assuming I'm still running that long myself.  

http://img.photobucket.com/albums/v443/jcp8832/GSvalvelogs.jpg

On the down side it's been an all time low in annual milage for me, just 6100 miles since last June's valve check.  I used to go 15-20k miles a year on my 97 GS.  

[burning1]

BTW... I am glad you did this experiment and post this thread. There are two big complaints I see about the GS over and over - Suspension, and Valve Check interval. It's nice to know that both are trivially corrected.

[piresito]

Sorry for digging up a zombie thread, but I never had the chance to thank gsJack for coming up with this!

Thanks! 

[piresito]

FYI,
Yesterday I went to the dealer to get shims, and the mechanic there told me that they use to set clearance at 0.10mm in the intake valves, and 0.15mm in the exhausts! He said that more than running with less stress, the bike would run smoother and provided a better response from the engine! The said mechanic, has 30 years experience, and he have read clearances on the GS500 with engine cool and after a dyno run. Curiously, after the dyno run, when hot, the clearances were tighter! 

[bombsquad83]

Good info piresito.  Validates what the community here has discovered.

[gsJack]

FYI,
Yesterday I went to the dealer to get shims, and the mechanic there told me that they use to set clearance at 0.10mm in the intake valves, and 0.15mm in the exhausts! He said that more than running with less stress, the bike would run smoother and provided a better response from the engine! The said mechanic, has 30 years experience, and he have read clearances on the GS500 with engine cool and after a dyno run. Curiously, after the dyno run, when hot, the clearances were tighter! 

All good to hear and I see nothing wrong with the mechanics choice of .10 mm intake and .15 mm exhaust clearances.  But that would be approximate since shims come in .05 mm increments and a .05 mm range would be required on a setting spec.  I set exhaust valves at .08-.13 mm and leave intake valves at the .03-.08 mm factory setting.  My 97 GS went 80k miles and my 02 GS has 97.5k miles on it both with the original factory shims on the intakes, the problem is with exhaust valves.

But I find it hard to believe the mechanic's clearances were tighter when hot after a dyno run.  It's been my experience they increase as the engine gets hot, confirmed by:

An exhaust valve went tight twice on my 97 GS requiring a 2 shim smaller change (.1 mm) to get adequate clearance.  When tight the engine would start and run rough for a minute and then smooth out as the clearance increased until the engine cooled again.

On my 82 CB750K with shim over bucket valves set at .002-.005" (.06-.13 mm) I actually checked them hot once and they all measured .015" or greater when hot.

I got my 02 GS with 4k miles on it and with a tight exhaust valve bucket and it measured .008" minimum when checked cold with the stuck bucket.  The bucket loosened and the engine smoothed out within a minute after cold startup as the engine heated.

On overhead cam engines with aluminum heads the aluminum head expands faster than the steel valves lifting the cams and increasing the valve clearances.

http://img.photobucket.com/albums/v443/jcp8832/GSvalvelogs.jpg

[Badot]

On overhead cam engines with aluminum heads the aluminum head expands faster than the steel valves lifting the cams and increasing the valve clearances.

This came to my mind first as well. Aluminum expands a little under twice as much as steel (12.3E-6/f in Al vs 7.3E-6/f in steel if I remember right).

And if you don't wait for your bike to cool off all the way before setting your valves they end up way too tight (from others' experiences).

If the GS is an exception, I'd be very curious as to why. The only reason I can think of would be if the bike wasn't fully warm for the dyno run and the heat sank out of the head faster than the valves... but that'd be one quick teardown.

[piresito]

On overhead cam engines with aluminum heads the aluminum head expands faster than the steel valves lifting the cams and increasing the valve clearances.

http://img.photobucket.com/albums/v443/jcp8832/GSvalvelogs.jpg

I allways tought that way too, but I have never measured the GS500 clearances after "hot". And with my limited experience, I would not argue with the mechanic about that!

You know, I asked me if I was using 0.03-0.08mm of clearance or 0.08-0.013, as I told him I was using the 8-13 in the exhaust, then he told me he used even higher (0.1 intake, 0.15 exhaust)!
So, I think we can say that the 0.08-0.13mm exhaust clearance range is safe, even if a bit larger than the 0.13mm mark, as we now know that there is people driving with even more than that!

[manosalx]

Hi all,

I am new here, owner of a 1992 GS500e. This is my first post.

I did my first valve check (79800km) and found the exhaust clearances to be 0,13 mm and 0,15 mm.

A very experienced mechanic (suzuki authorized) who was responsible for its maintenance the past 12 years told me NOT to decrease the exhaust clearances being out of the service manual limits.

He suggested I could keep the in valves in service manual limits but NOt the exhaust valves.

He explained the reason:

If someone drives for some time in low RPM (like me) there is a very small "smoke fog" built up in the exhaust valve seating (small film of smoke). This makes clearnces increase a bit. But he told me that if you open up your GS in a hard ride with high RPM (especially using 100 octane fuel) the smoke fog gets cleared from valves seating and the clearances decrease.

He says he has seen many bikes setting the exhaust valve clearances set on official setting (with fog eveloped) and then after a hard ride the seatings are cleared and clearances get so tight that burn the valves.

I trust him because he held this bike for 12 years with exactly zero problems and high engine performance.

I should also mention that in this bike, whose history I know since previous owner is my closest friend, did about 25000km with valve clearances not changed at all from the previous settings!

I vote for high exhaust valve clearnces ( up to 0,15 mm) and intake clearances above 0,05

[The Buddha]

The only down side to running them loose (and you're at 3X for exhaust and 2X for intake) is that the valve train noise might prevent you from hearing other noises, like when my alternator rotor was hitting the stator, it took me a long while and only when I had the bike shaking and vibrating more I found the problem. Else its all good.
Cool.
Buddha.

[Bluesmudge]

I vote for high exhaust valve clearnces ( up to 0,15 mm) and intake clearances above 0,05

This seems to be the consensus around here. Different people have different maximum clearances they are comfortable with but generally .13 to .15 maximum. I generally shoot for .05 -.08 on intake and .07 -.13 on exhaust. If I don't have the exact right shim I have also run all the way out to .15 without any noticeable issues.

[manosalx]

Thanks for the info!